Mosquito ancestry shapes chikungunya and dengue risk across the Mediterranean

The Asian tiger mosquito, Aedes albopictus, has earned its reputation as one of the world’s most hazardous invasive species. Since first establishing itself in the Mediterranean Basin in the early 1980s, it has spread across southern Europe and become increasingly implicated in local, or autochthonous, transmission of chikungunya and dengue viruses in regions where these diseases were once exclusively travel-associated. A new study published in Parasites & Vectors now shows that the mosquito’s tangled colonization history is not just a curiosity of population genetics: the genetic ancestry of individual Mediterranean populations significantly shapes how competently they can acquire, disseminate and transmit chikungunya virus (CHIKV), dengue virus (DENV) and Zika virus (ZIKV), effectively redrawing the map of arboviral risk across Europe.

The research, led by Riccardo Piccinno and Anna Rodolfa Malacrida of the University of Pavia, together with colleagues at the Institut Pasteur in Paris and partners in Switzerland, Italy and the Balkans, set out to answer a deceptively simple question: do genetically distinct mosquito populations differ in their ability to transmit arboviruses? The answer, the authors report, is a clear yes, and the pattern they uncovered is striking. Neighboring mosquito populations with different genetic ancestries showed drastically different competence profiles for CHIKV and DENV, while geographically distant populations that share ancestry behaved similarly. In other words, for these viruses, where a mosquito’s genes came from matters more than where the mosquito lives.

To reach that conclusion, the team combined two complementary lines of evidence: population genetics and experimental vector competence assays. On the genetic side, they genotyped mosquitoes from an ancestral reference population in Guangzhou, China, and from ten adventive populations sampled across five Mediterranean regions, spanning Southern Switzerland, Northern and Central Italy, the Balkans and Greece. The markers of choice were highly polymorphic simple sequence repeats, or SSRs, which allow fine-scale discrimination of genetic lineages. Using the Bayesian clustering program STRUCTURE, the researchers assigned individuals to ancestry groups, and with the approximate Bayesian computation framework DIYABC-RF they reconstructed the demographic histories that produced the present-day genetic mosaic.

That history, the study finds, was anything but a single clean invasion wave. By combining historical records with demographic modeling, the authors show that the establishment of Aedes albopictus in the Mediterranean was driven by chaotic, discontinuous introductions of distinct lineages, followed by admixture events in which previously separated genetic backgrounds interbred. The result is high heterogeneity in both space and ancestry: populations separated by only a few hundred kilometers can carry markedly different genetic compositions, reflecting separate introduction routes, likely via the international trade in used tires and other commodities that has repeatedly ferried mosquito eggs across borders. This genetic patchwork, rather than a homogeneous expansion front, is the biological backdrop against which viral transmission now plays out.

The experimental half of the study measured vector competence using the standard trio of quantitative indices. Infection rate captures the proportion of mosquitoes in which the virus successfully establishes an infection in the midgut after an infectious blood meal; dissemination efficiency measures how many of those infected mosquitoes allow the virus to escape the midgut and spread to secondary organs, including the salivary glands; and transmission efficiency quantifies the fraction with virus present in the saliva, the prerequisite for onward transmission to a new host. Mosquitoes from each population were fed blood meals containing CHIKV strain 06.21, DENV-1, or ZIKV strain PE243, and these indices were scored at multiple days post-infection, specifically 7, 14 and 21 days, to track the temporal progression of infection.

Statistical analysis then linked the genetic and virological datasets. Univariate and multivariate models assessed whether population identity, ancestry group membership, and days post-infection were associated with each competence index. For CHIKV, the analyses identified day post-infection, population, and two ancestry components as significant factors associated with infection, with some ancestry fractions showing positive associations and others negative ones. For DENV, population and three ancestry components were significantly associated with infection rate, although the authors note that two of these lacked a biologically plausible monotonic trend across ancestry categories, meaning higher ancestry fractions did not simply translate into higher infection rates. For ZIKV, by contrast, no variable emerged as a significant predictor, suggesting that the genetic heterogeneity captured in this study does not translate into measurable variation in Zika competence among these populations.

The most consequential finding concerns CHIKV and DENV. Ancestry and population identity significantly influenced dissemination and transmission as well as infection, and the geographic pattern was counterintuitive: proximity did not predict similarity. Populations in neighboring geographical areas but with distinct ancestries exhibited drastically different competence profiles, whereas geographically distant populations sharing genetic ancestry displayed similar vector competence. This dissociation between geography and genetics implies that the introduction history of each local population, not local environmental conditions alone, has left a durable imprint on its capacity to transmit these viruses. It also suggests that the genetic variants governing viral infection and dissemination vary among source lineages, so that admixture has produced a mosaic of transmission potential across the region.

The public health implications are direct. Europe has experienced a rising trend of both imported and autochthonous arboviral infections in recent years, with chikungunya and dengue outbreaks recorded in Italy, France and elsewhere. If the mosquitoes buzzing in one province are substantially more competent vectors than those in the next, then uniform, region-wide control assumptions may misallocate resources. The authors argue that their results underscore the urgent need for localized, geographically tailored vector control strategies in Europe, in which surveillance and intervention intensity are calibrated to the actual transmission potential of local mosquito populations rather than to a generic regional estimate.

Methodologically, the study demonstrates the value of integrating fine-scale population genomics with standardized vector competence assays. The SSR-based genotyping, combined with STRUCTURE clustering and DIYABC-RF demographic inference, allowed the team to move beyond simple labels of origin and to quantify ancestry fractions within admixed populations. The logistic regression framework then made it possible to test the contribution of each factor while accounting for others, including the strong temporal effects of days post-infection that are well known to shape competence measurements. Supplementary analyses reported pairwise genetic differentiation among populations and detailed infection, dissemination and transmission rates stratified by virus, time point and population, providing a transparent record of the underlying data.

The work also carries broader lessons for invasion biology. Aedes albopictus is a textbook example of how global trade creates repeated, genetically diverse introductions, and this study shows that such demographic chaos can have functional consequences for disease transmission. As the climate warms and the mosquito’s suitable habitat expands northward, new introductions and further admixture are likely, potentially reshaping vector competence in currently lower-risk areas. Understanding the provenance of each new population, the authors suggest, should therefore become part of the risk-assessment toolkit, alongside entomological surveillance and case monitoring, if Europe is to anticipate rather than merely react to the next arboviral emergence.

Subject of Research: Vector competence and population genetics of invasive Aedes albopictus mosquitoes in the Mediterranean Basin

Article Title: Provenance and competence for CHIKV and DENV of Aedes albopictus populations

Article References: Piccinno, R., Madec, Y., Mariconti, M., Fiorenza, G., Carraretto, D., Forneris, F., Flacio, E., Coletti, S., Gasperi, G., Failloux, A.-B., & Malacrida, A. R. (2026). Provenance and competence for CHIKV and DENV of Aedes albopictus populations. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07705-6

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07705-6

Keywords: Aedes albopictus, Asian tiger mosquito, vector competence, chikungunya, dengue, Zika, population genetics, Mediterranean Basin, invasive species, arboviruses, genetic ancestry, vector control